1. Field of the Invention
The present invention relates to a dual-port input equalizer, and more particularly, to a dual-port input equalizer capable of sharing common circuit elements.
2. Description of the Prior Art
With advanced development in technology, various high speed signal transmission interface technologies, such as digital visual interface (DVI), high definition multimedia interface (HDMI), etc., have been presented and are utilized widely in communication, storage, or image processing systems. Therefore, many electronic products for daily life, such as multimedia players, set-top boxes, game consoles, home audio/video equipment, personal computers, portable apparatuses, etc., are equipped with such signal transmission interfaces for inputting or outputting various audio and image data.
In general, channel attenuation and inter-symbol interference (ISI) effect for the transmitted signals are becoming serious concerns with increasing transmission channels, both of which reduce the quality of the transmitted signal. Therefore, an equalization process is utilized at the receiving end for compensating attenuation and canceling the ISI effect for the transmitted signal. Please refer to FIG. 1. FIG. 1 is a schematic diagram of an equalizer 10 according to the prior art. The equalizer 10 is able to compensate channel attenuation of the differential signals (input signals VIN1 and VIN2) transmitted from the cable and cancel the ISI effect of the differential signal. The equalizer 10 includes a first transistor M1, a second transistor M2, resistors R1, R2, R3, capacitor C1, a first current source IS1, and a second current source IS2. The interconnections of the units are as shown in FIG. 1. In the equalizer 10, the first transistor M1 and the second transistor M2 are n-type metal oxide semiconductor transistors, respectively, which are utilized for outputting signals VO1 and VO2 according to input signals VIN1 and VIN2. In addition, the resistors R3 and the capacitor C1 are coupled between the source of the first transistor M1 and the second transistor M2 in a parallel manner to form a common mode structure. The first current source IS1 and the second current source IS2 can derive current from the source of the first transistor M1 and the second transistor M2 for operation.
However, with the diversity of electronic products, the product design needs to satisfy many possible requirements. For example, two or more receiving ports of the HDMI transmission interface may be designed in an electronic product for receiving various signals from different sources. For the conventional circuit scheme, the amount of the equalizers should depend on the amount of the signal sources. In such a condition, the components of the equalizers, such as the load portion (resistors R1, R2), the zero-point generation circuit (resistors R3 and capacitor C1), and the current source IS1 and IS2 will occupy much circuit area, and the circuit area may increase in multiples with the increased amount of the signal sources, thus increasing the difficulty of system design and manufacturing cost.